1. Technological Field
The present disclosure relates generally to circuit elements and more particularly to devices for the sensing of arc fault currents, and methods of utilizing and manufacturing the same.
2. Background of the Invention
An arc fault is a high power discharge of electricity between two or more conductors. This discharge generates heat, which can break down the wire's insulation and ignite nearby flammable material thereby causing a fire. Arc faults range from a few amperes to thousands of amperes and generate a detectible broadband electrical signature. This signature can typically range from 100 Hz to 1 GHz depending on the bandwidth of the electrical system in which the arcing occurs.
The danger of arc faults has been recognized since the widespread use of electricity. The U.S. Consumer Product Safety Commission (CPSC) recognized in the latter part of the 20th century the majority of the high U.S. fire death rate was caused by residential fires of electric origin. During the 1990's arc fault detection and circuit interruption technology reached commercial feasibility. Underwriters Laboratories (UL) and the National Electrical Manufactures Association (NEMA) recognized the need for, and produced standards for, Arc Fault Circuit Interrupters (AFCIs) similar to overload circuit breakers. The National Electric Code began requiring Arc Fault Circuit Interrupters (AFCIs) in bedroom circuits in 1999. NEC has recently expanded the AFCI requirement to circuits in all living spaces as well as in photovoltaic solar (PV) installations due to the danger from PV DC arc faults. The recent UL Standard 1699, Arc Fault Circuit Interrupters, defines the requirements for UL certification of AFCIs which interrupt a circuit (similar to a circuit breaker) when an arc fault signature is detected in the circuit.
Modern AFCIs are composed of an arc fault sensor component, detector circuitry, and an electrical circuit interruption mechanism. Electrical distribution system AFCIs are typically integrated in circuit breakers and AC plug-ins/receptacles. For PV systems, the AFCIs are integrated in string inverters, DC equalizers, microinverters, and combiner boxes.
To provide electrical isolation between the arc fault current carrying conductor and the AFCI sensor components, most of the arc fault sensors used in AFCI systems are toroidal current transformers (CTs) with a magnetic core or toroidal Rogowski coils (RCs) with no magnetic core packaged inside a toroidal plastic housing. These AFCI sensors present a number of problems:                1) They tend to be large (several centimeters in diameter and a centimeter high), much too large for the thin (e.g., 0.5 inch) circuit breakers, AC receptacles, and PV combiner boxes, microinverters, and DC equalizers.        2) The primary (conductor carrying the arc fault signal to be sensed) must be routed through the center of these AFCI sensor toroids. Such routing limits flexibility, is inconvenient, and expensive.        3) The bandwidth of CTs (<1 MHz), Rogowski Coils (<10 MHz) is much less than the bandwidth of the arc fault signals being sensed which causes them to act like low pass filters and limits the performance of the detection circuits.        4) Arc fault sensor toroids are expensive compared to the miniature arc fault current sensor. In addition to the external plastic toroidal container, CTs require a magnetic core large enough so that it does not saturate with the normal AC and DC currents of the application and hundreds of turns of copper wire. Rogowski coils also require hundreds of turns of precisely wound copper wire and extra electrical amplification for their low signal output.        
The increasing application of AFCIs require a sensor component without the above-referenced shortcomings that is small enough to be deployed near or between adjacent traces on a printed circuit board (PCB) while having sufficient output to support arc fault detection circuitry.